Various blood processing systems now make it possible to collect particular blood constituents, instead of whole blood, from a blood source. Typically, in such systems, whole blood is drawn from a blood source, the particular blood component or constituent is separated, removed, and collected, and the remaining blood constituents are returned to the blood source. Removing only particular constituents is advantageous when the blood source is a human donor, because potentially less time is needed for the donors body to return to pre-donation levels, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for transfer and/or therapeutic treatment.
Whole blood is typically separated into its constituents through centrifugation. This requires that the whole blood be passed through a centrifuge after it is withdrawn from, and before it is returned to, the blood source. To reduce contamination and possible infection (if the blood source is a human donor or patient), the blood is preferably processed within a sealed, sterile fluid flow system during the centrifugation process. Typical blood processing systems include a disposable, sealed, and sterile flow circuit, including a centrifuge chamber portion, that is mounted in cooperation on a durable, reusable assembly containing the hardware (centrifuge, drive system, pumps, valve actuators, programmable controller, and the like) that rotates a centrifuge chamber and controls the flow through the fluid circuit.
The centrifuge rotates the centrifuge chamber of the disposable flow circuit during processing. As the centrifuge chamber is rotated by the centrifuge, the heavier (greater specific gravity) components of the whole blood in the centrifuge chamber, such as red blood cells, move radially outwardly away from the center of rotation toward the outer or “high-G” wall of the centrifuge chamber. The lighter (lower specific gravity) components, such as plasma, migrate toward the inner or “low-G” wall of the centrifuge chamber. The boundary that forms between the denser red blood cells and the lighter plasma in the centrifuge chamber is commonly referred to as the interface. Various ones of these components can be selectively removed from the whole blood by providing appropriately located channeling structures and outlet ports in the flow circuit. For example, in one blood separation procedure, plasma is separated from cellular blood components and collected, with the cellular blood components and a replacement fluid being returned to the blood source. Alternatively, red blood cells may be harvested from the centrifuge chamber and the rest of the blood constituents returned to the donor. Other processes are also possible including, without limitation, platelet collection, red blood cell exchanges, plasma exchanges, etc. In these procedures, the efficiency of the process is often dependent upon accurate identification and control of the position of the interface during centrifugation.
It is known to employ an optical sensor system to monitor the flow of blood and/or blood components through the flow circuit in the centrifuge and determine various characteristics of the flow. For example, U.S. Pat. No. 6,899,666 to Brown relates to an optical sensor system for viewing into the centrifuge chamber for detecting and controlling the location of an interface between separated blood components in a centrifuge. While this system functions satisfactorily, there remains an opportunity to provide optical monitoring systems with improved interface detection and greater robustness.